Rule of Three Calculator
A corresponds to B. What corresponds to C? → X
X =0
Proportional: X = B ÷ A × C. Inverse: X = A × B ÷ C.
Solve the rule of three quickly
The rule of three is the classic method for calculating a fourth value from three known ones. The calculator supports both variants: the proportional and the inversely proportional rule of three.
- Proportional: More means more. Example: 3 apples cost €12, what do 5 apples cost? → €20.
- Inverse: More means less. Example: 3 workers need 12 hours, how long do 5 need? → 7.2 hours.
- Formula: Proportional X = B ÷ A × C, inverse X = A × B ÷ C.